feat(GlDrawer): add sticky footer

What does this MR do?

This MR resolves #1811 (closed).

New requirement based on this review

It is important to have sticky footer

1. I used relatively new css property sticky to push footer to bottom.
2. Property sticky respects dimensions of siblings, stays in viewport on scroll and won't cover scrolling body of a drawer as it could be with absolute or fixed,so there is no need to add extra padding to drawer body based on footer height.
3. Drawer should have display flex with flex-direction column
4. Drawer-body have flex-grow: 1, so it is stretched between between header and footer and footer stays on bottom even when list is short

It shouldn't affect existing codebase in gitlab anywhere where GlDrawer is used.

Example 1
header_footer

Example 2
other_options

Here example in design how it is planned to be used.

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines.
• GitLab UI's contributing guidlines.
• If it changes a Pajamas-compliant component's look & feel, the MR has been reviewed by a UX designer.
• If it changes GitLab UI's documentation guidelines, the MR has been reviewed by a Technical Writer.
• If the MR changes a component's API, integration MR(s) have been opened in the following projects to ensure that the @gitlab/ui package can be upgraded quickly after the changes are released:
  • GitLab: mr_url
  • CustomersDot: mr_url
  • Status Page: mr_url
• Added the ~"component:*" label(s) if applicable.

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• Security reports checked/validated by a reviewer from the AppSec team

Accessibility

If this MR adds or modifies a component, take a few moments to review the following:

• All actions and functionality can be done with a keyboard.
• Links, buttons, and controls have a visible focus state.
• All content is presented in text or with a text equivalent. For example, alt text for SVG, or aria-label for icons that have meaning or perform actions.
• Changes in a component’s state are announced by a screen reader. For example, changing aria-expanded="false" to aria-expanded="true" when an accordion is expanded.
• Color combinations have sufficient contrast.

Closes #1811 (closed)